Compound Adjectives

Form

A compound adjective is two or more words working as a single adjective, and in front of a noun they are joined with hyphens: “a well-respected scientist”, “a family-friendly restaurant”, “a last-minute decision”.

Before a noun, a number compound keeps the noun inside it singular — “a six-hour surgery”, not “a six-hours surgery” — and an age compound takes hyphens all the way through: “a ten-year-old house”. Never hyphenate after an adverb ending in -ly, because the -ly already shows which word it belongs to ('a highly regarded institution', 'a mutually beneficial agreement'). After the verb, most compounds lose the hyphen ('a high-quality product', but 'The product is high quality'), while the ones the dictionary lists with a hyphen, such as self-made and thought-provoking, keep it wherever they stand.

When to Use It

1. 1

   Hyphenate when the compound sits directly in front of the noun it describes

   She gave a well-thought-out answer.

2. 2

   Keep the noun inside a number compound singular

   She submitted a 3,000-word essay.

3. 3

   Before a noun, hyphenate every part of an age compound, as in “They adopted a two-year-old dog” — after the verb it opens up again

   The dog is two years old.

4. 4

   Leave out the hyphen after an -ly adverb

   It was a highly regarded institution.

5. 5

   Usually drop the hyphen when the compound comes after is, are, was or seems, unless the dictionary lists it hyphenated

   The documentary was thought-provoking but The product is high quality.

Common Mistakes

• Making the noun inside a number compound plural: write a four-star hotel, not a four-stars hotel, because the compound works as one adjective, not as a count.
• Leaving an age compound half-hyphenated: write a five-year-old child, not a five-years-old child, because every part of the compound joins up before a noun.
• Hyphenating after an -ly adverb: write a highly regarded institution, not a highly-regarded institution, because the -ly already shows that “highly” belongs to “regarded”.
• Dropping the hyphen in front of the noun: write a two-bedroom apartment, not a two bedroom apartment, because the hyphen shows that “two” and “bedroom” form one unit.
• Leaving a multi-word compound open: write a well-thought-out answer, not a well thought out answer, because the hyphens show that “well”, “thought” and “out” work together as one adjective.